1. Field of the Invention
This invention relates to a color printing method, and more particularly to a color printing method in which primary object illuminating light is guided for exposure to a color film, which is also exposed to object image forming light, and then recorded thereon to produce an optical density after the color film has been developed, the optical density being used to determine blue, green and red exposures for the picture frame carrying the object image when the color print is intended to be produced with a color positive photosensitive material.
2. Description of the Prior Arts
The description will first be given to a method, which has been put to practical use to mass-produce color prints, for producing color positive pictures from color negatives on a color photgraphic paper by means of a full-correction type automatic color printer.
This automatic color printer operates according to a method "Integrating to Gray" proposed by Evans in U.S. Pat. No. 2,571,697 . In this method, three colors (blue, green, red) all over a picture on the color negative are measured to obtain their optical density, on the basis of which three color lights, to which a positive photosensitive material is exposed, are determined so that the three color lights may be equal to one another on the color positive photosensitive material, that is, they become thereon a neutral gray. In other words, the automatic color printer using the Integrating to Gray has its exposure conditions so determined that a proper color print can be obtained from a standard color negative. The proper color print can, however, not be obtained from negatives having color failure and/or density failure, particularly from the following negatives:
(1) a color negative obtained by photographing under a light source having a color temperature different from that of a light source by which the standard color negative is produced; (2) a color negative film differing greatly from the standard color negative in three-color density composition; and (3) a color negative film differing greatly from the standard color negative in density distribution, particularly in color density distribution.
The printing from the color negative having such color failure and/or density failures with the aid of the Integrating to Gray results in the production of a positive print whose color and/or density are out of balance.
In this respect, the full-correction type automatic color printer is typically provided with color correcting buttons, density correcting buttons or the like for conducting correction such as low-ward correction or slope control in order to also obtain a proper color print from the above-mentioned color negative having the color failure and/or density failure.
Recently, a terminal device is further partially utilized, in which the color negative is divided in small units for density measurement to determine the exposure conditions in cooperation with a computer. Such an automatic printer and its terminal device are, however, very complicated in structure and sophisticated in operations, and produces a color print whose quality and yield have not been so satisfactory as expected.
There is, on the other hand, another method in which a gray scale is disposed at an object in the photographing step and recorded on the color film together with the object. In this case, the exposure conditions in the automatic color printer are so determined that the gray scale can be reproduced on the color print with non-coloration, i.e., gray while the object can be reproduced with the most suitable density. This method makes it possible to obtain the proper color print of all the objects so far as the gray scale can be photographed together with the object and the density of the gray scale can be detected to determine an amount of exposure.
In practice, however, it is impossible to put this method to practical use, because no common photographer generally disposes the gray scale at the object in the photographing step.